Orchid Phytophthora Disease: Prevention and Control Methods and Practical Experience Sharing

　　OrchidPractical Prevention and Control of Phytophthora Disease (including stem rot) Phytophthora disease: The pathogen of Phytophthora disease is the oomycete fungus Phytophthora. This disease is one of the worldwideorchiddiseases. It had not previously appeared in our country, but in recent years it has occasionally occurred in localized areas. The parts infected by the Phytophthora fungus show wet rot, turning black after drying, which is why it is also called "black rot." Although Phytophthora disease and black rot have the same lesion color in the late stage, the affected parts and early lesion color of Phytophthora disease differ. Phytophthora disease mostly starts from the middle section of the lateral margin of mature leaves. However, it can vary depending on local climate and ecological conditions. In some cases it may start from the leaf base or leaf tip, and in others the roots, stems, leaves and flowers may all be affected. In the early stage of infection, the leaf color remains unchanged; the affected area looks as if it has been crushed and bruised, wet-looking, and dark green; after drying, it turns black. The parts of the tissue not directly affected wither and turn black because the vascular tissue is destroyed. OrchidPhytophthora disease, also commonly known as "water damage," is a fungal disease caused by infection with Phytophthora cactorum and Pythium ultimum among the plant monospore fungi. Because of differences in the site of occurrence and the symptoms produced, it can also be divided into black rot, heart rot, stem rot, damping-off, and so on. Infection by Phytophthora cactorum readily causes root rot, damping-off and crown rot, while infection by Pythium ultimum causes root rot and damping-off of the plant. When the young shoots near the leaf base of Chinese orchids are infected, the leaf color initially fades or becomes water-soaked, then gradually expands into light brown to dark brown decay, until the entire plant dries up and dies. The symptoms are not easily distinguished from southern blight and Fusarium-induced basal rot. In the warm climates of the southern regions, it can occur in allfour seasonsof the year, but it is most severe in spring during the plum rain season under conditions of high humidity, poor ventilation and insufficient sunlight. The pathogen can spread through splashing rain, and can also be transmitted by snails, slugs and other feeding insects. To prevent and control orchid Phytophthora disease, care should be taken in normal times to avoid excessive water and to ensure good ventilation and ample sunlight. In the early stage of the disease, a sterilized blade should be used to excise the diseased tissue, and 70% mancozeb wettable powder at 600-800 times dilution or 25% metalaxyl wettable powder at 500-800 times dilution should be sprayed. Apply once every 7 days, for 2-3 consecutive times. Severely affected individual plants should be immediately removed and destroyed. In normal times, attention should also be paid to controlling damage by snails and slugs to prevent the spread of Phytophthora disease. I hope this is useful to beginners.